1. Field of the Invention
This invention relates to a microwave dual reflector antenna. More particularly, the invention provides a self supported feed cone radiator for such antennas suitable for cost efficient manufacture via injection molding.
2. Description of Related Art
Dual reflector antennas employing self-supported feed direct a signal incident on the main reflector onto a sub-reflector mounted adjacent to the focal region of the main reflector, which in turn directs the signal into a waveguide transmission line typically via a feed horn or aperture to the first stage of a receiver. When the dual reflector antenna is used to transmit a signal, the signals travel from the last stage of the transmitter system, via the waveguide, to the feed aperture, sub-reflector, and main reflector to free space.
The electrical performance of a reflector antenna is typically characterized by its gain, radiation pattern, cross-polarization and return loss performance—efficient gain, radiation pattern and cross-polarization characteristics are essential for efficient microwave link planning and coordination, whilst a good return loss is necessary for efficient radio operation.
These principal characteristics are determined by a feed system designed in conjunction with the main reflector profile.
Commonly owned U.S. Pat. No. 6,107,973, titled “Dual-Reflector Microwave Antenna” issued Aug. 22, 2000 demonstrates a feed assembly wherein a sub-reflector is supported by a dielectric funnel coupled to the end of a supporting waveguide. Functioning as a support structure only, the dielectric funnel becomes an impedance discontinuity that must be compensated for as the sub-reflector and reflector dish surface profiles and diameters, alone, are utilized to shape the RF path, resulting in an increased diameter of the sub-reflector and/or reflector dish. As the sub-reflector dimensions increase, RF signal path blockage by the sub-reflector along the boresight of the reflector antenna becomes significant. Further, an increased overall dimension of the resulting reflector antenna requires additional reinforcing structure considerations for both the reflector antenna and support structures the reflector antenna may be mounted upon.
Deep dish reflectors are reflector dishes wherein the ratio of the reflector focal length (F) to reflector diameter (D) is made less than or equal to 0.25 (as opposed to an F/D of 0.35 typically found in more conventional dish designs). An example of a dielectric cone feed sub-reflector assembly configured for use with a deep dish reflector is disclosed in commonly owned U.S. Pat. No. 6,919,855, titled “Tuned Perturbation Cone Feed for Reflector Antenna” issued Jul. 19, 2005 to Hills, hereby incorporated by reference in its entirety. U.S. Pat. No. 6,919,855 utilizes a dielectric block cone feed with a sub-reflector surface and a leading cone surface having a plurality of downward angled non-periodic perturbations concentric about a longitudinal axis of the dielectric block. However, the plurality of angled features and/or steps in the dielectric block requires complex machine tool manufacturing procedures which may increase the overall manufacturing cost.
Therefore it is the object of the invention to provide an apparatus that overcomes limitations in the prior art, and in so doing presents a solution that allows such a feed design to provide reflector antenna characteristics which meet the most stringent electrical specifications over the entire operating band used for a typical microwave communication link.